Reactance tube circuitry



April 23, 1957 A. c. ARMSTRONG 'EIAL 2,790,147

" REACTANCETUBE CIRCUITRY' Filed Oct. 23, 1953 s Sheets-Sheet 1 PIC-3.25

2 F I a. 4B

5. INVENTORS l4 ALBERT CLAUDE ARMSTRONG JOSEPH WARREN KEE AGENT A. c. ARMSTRONG ETAL 2,790,147

REACTANCE TUBE cmcurmv April 23,-1957 s Sheets-Sheet 2 Filed Oct. 2 3, 1953 FIG. 5A

FIG. 5B

FIG

PIC-3.7

- INVENTORS ALBERT CLAUDE ARMSTRONG JOSEPH WARREN K EE BY W 0M8.

AGENT P 23, 1957 I A. c. ARMSTRONG ETAL 2,790,147

REACTANCE TUBE CIRCUITRY Filed Oct. 23, 1953 3 Sheets-Sheet 3 Fl 0. a

I I r" I I 4 I I INVENTORS ALBERT CLAUDE ARMSTRONG JOSEPH WARREN KEE BY M'C AGENT United States Patent 2,790,141 REACTANCE TUBE cmcumzv Albert Claude Armstrong, Takoma Park, Md., and Joseph Warren Kee, Monrovia, Califi, assignors to Vitro Corporation ofAmerica, Verona, N. J.

Application October 23, 1953, Serial No. 387,868

16 Claims. (ill. 332-28).

Our invention relates to oscillator frequency modulation appa-ratus'and more particularly relates to reactance tube circuitry for use with. such apparatus.

In many electronic applications, it is necessary to shift the frequency of an oscillator above and below its nature! 'or central frequency in accordance with the instantaneous value of an incoming modulating signal. One method ofdoing this is to vary the r-eactance of the oscillator tank circuit, thus changing the oscillator frequency. Another method is to inject a variable current into the tank circuit which. is in phase with the current; in a selected reactive element within the tank while maintaining the voltage across the tank substantially constant. While the injection method. does not physically change the reactance values within the tank, it produces the same effect by changing the apparent reactance values, thus changing-the resonant frequency of the tank accordingly.

- It is conventional to use a reactance tube as a current injection device. The reactance tube, which is generally a pentode, is connected so that its plate-cathode circuit shunts the tank circuit of the oscillator. Aphase shifting network consisting of a resistor and capacitor connected in series also shunts the tank circuit, and'the junction of this resistorand capacitor is connected to a first control gridiof the tube. The relative values of the resistor and capacitor'are chosen so that thevolta-ge at this. grid is shifted almost 90 with respect to the voltage on the plate. An incoming modulating signal is supplied tothe second'con'trol' grid and changes the plate current of the tube accordingly. By virtue of the phase: shifting network, the plate current is maintained substantially in quadrature with the plate voltage and this quadrature cur rent can be injected into the tank circuit in the manner outlined in the-preceding paragraphf" I However, this reactance tube circuit has serious disadvantages. Since the phase shiftingnetworkdescribed above must contain some appreciable resistance and since the capacitor itselfmust have some resistance, the phase shift-between the first grid and plate must always be lessthan 90. Consequently, there is a real, component of voltage appearing at the first grid which introduces a plate current component which is in phase with the plate'voltage This component when injected into the tank circuit, acts as. an apparent resistance which changes the Q'of the tank and causes amplitudernodul-a: tion of the frequency modulated output signal firom the oscillator,

Moreover, since the reactance of the phaseyshifting network must varywith frequency, the phase shift between the first grid and the plate is variable, and the magnitude of the voltage which is. fed back from the plate to the gridjs variable so that the value of the apparent resistance is. continuously changing; ccnsequently, the percentage of amplitude modulation is not fixed but is continuously variable. 7 l V Since this amplitude modulation notonly modifiesgthe a phase shift to exactly for any one oscillator tre .tudemodulation from appearing.

Patented Apr. 23, 19 57 power distribution in the side 'bands. of. the oscillator output signal but. also. causes. distortion in the modulation on the carrier, itis highly desirable to prevent such amplb We have invented animproved reactance tube arrangeparent resistance and thus'prevents the undesirableamp-litude modulation.

Accordingly, it is anobject of the present invention to provide improved react-ance tube circuitry of the character-indicated.

Another object is. toprovide improved reactancetube circuitry in which the tube gridaplate phase shift adjustable and can. be set-to exactly 90 at any frequency. Still another object is to provide i-mpnoved reactance tube circuitry which. includes .an adjust-able phase shifting network capable of providing a tube g-ridplate phase shift in excess of- 90.

Yet another object is to provide improved reaotance tube circuitry which includes a phase shifting network capable of delivering a feedback voltage to the grid of the tube whose magnitude is independent of frequency. A further object is to provide improved react-ance tube circuitry which employs a single-ended reactance' tube. Still another object is to provide improved reactance tube circuitry which employs abalance push-pull reactance tube-arrangement. V

These and other objects of the invention will be explained or will become apparentto those skilledin the art when this specification-is read inconjunction-with the accompanying drawings wherein:

Figure 1 shows a single-ended reac'tance tube circuit which illustrates one form ofthe invention;

Figures 2A and 2B are vector diagrams of the voltage relationships established by the circuit shown in Figure "1'; Figurcs 3A and 3B show respectively a first variant of the circuit shown-in Figure 1 and a vector'diagnam for the first variant;

Figures 4A and 4B show-respectively a second variant of the circuit shown in Figure land a vector diagram for the second variant; 7

Figures 5A- and 5B show respectively a third variant of thecircuit shown in'Figure 1 and a 'vector'diagram forthe thirdvariant; L Figure 6 shows a fourth variant of the circuit shown in Figure 1;

Figure 7 shows a pushpull reactarnce tube circuit which illustrates a second form of the invention;

Figure 8- shows a variant of the circuit shown in Figure 7; and

Figure 9 shows a push push reactance tube circuit whichillustrates-a third; form of theinvention.

Brieflystated, our invention contemplates an oscilla tor having a frequency determining tank circuit including acap-acit-ance shunted by an inductance. A network including resistance and reactance elements connected in series isconnected across the inductance. We provide a reactance -tube, which preferably is a pentode but which may be any high vacuum tube havingfat least one control grid, whose anode-cathode circuit is connected across the inductance. The control grid cathodecircuit of the tube is connected between the junction of the elements in the network and a point on the inductance-which is intermediate to the ends. By virtue of this arrangement,

and by suitably choosing the values of the reactance and resistance elements, it is possible to adjust the grideplate quency. v In addition, the properties of the phase shift network are such that thema gnitude of the voltage feedback-for the plate to thegrid remainssubstantially constantxand is independent of frequency. o

-Jlhe modulating signal which is .to modulate the frequency of the oscillator output signal may be applied either to the control grid or another grid. This single tube arrangement greatly reduces the magnitude of the apparent resistance injected into the tankcircuit.

In order to obtain substantially complete cancellation of this injected resistance as well as to obtain additional circuit stability and sensitivity, we provide a second 'react- -ance tube whose plate-cathode circuit. isiin push-pull or push-push connection with the corresponding circuit of the first tube and whose control. grid-cathode circuit is .conn'ected toa secondnetwork shunting the gtankcircuit.

1'11 lthis.,situation,. the modulatingsignal is;fed in Zpushanode-cathode circuit ofthisvalveis connected between -,terminals 4 and 5 which are in turn connected to opposite ends of an inductance 7. Inductance 7 shunts capacityv 8 to form resonant circuit 9 therewith. This circuit is the tank,circuit of a conventional oscillator 1.

The midpoint 10 on inductance 7 is connccted. through terminal 6 and capacitor '16 to, the cathode 11 of. valve 3. Tiheseries combination'of a fixed resistorlZ and ,a variable capacitor 13 is connected bewteen terminals 4, and. 5. The junction 14 of resistor 12 and capacitor 13.1nay. be connected to grid Z of valve 3 but, in this example, is connec to g 15-- J. .2.

In order to understand the operation of this circuit arrangement, it will be necessary to refcrnto the vector diagram shown in Figure 2A. The voltage developed across inductance 7 appears between terminals 4 and 5 and is identified as voltage The voltage produced across the terminal 4 and 6 is in phase with voltage A and; is equalin magnitudeto one half this voltage; this produced voltage is identified as voltage B. The sum of the voltages developed between terminals 4 and 14 (the voltage across resistor 12 identified as voltagejC); and terninals 14 and 5 (the voltage across capacitor 13 identifiedas voltage D) must be equal to voltage A, Therefrequency is shifted As this angle varies from 90 a small component of voltage E is developed which is either in phase or opposed in phase with voltage A and is capable of introducing a resistive component into circuit 9.

Figure 2B shows the relationships between voltages when the frequency of oscillator 1 is increased beyond its central frequency. The reactauce of capacitor 13 decreases, so that the magnitude of voltage D decreases. When voltage A is constant, as in this case, the sum of voltage C and D remains constant, so that voltage C increases. Consequently, the phase angle between voltage E and voltage A is decreased; andvoltage F, which is a component of voltage E, is developed which is in phase with voltage A. The resistance component thus intro duced is negative.

If the oscillator frequency were decreased below the central frequency, the phase angle would be larger than 90, voltage component F'would be in phase opposition with voltage A, and the resistive component is positive.

In either situation, however, the resistance component is much, reduced ascompared to prior systems of this kind.' For example, the magnitude of the voltage fed back fromthe plate to the grid is maintained substantially constant so that this voltage does not introduce a variable resistance component into the tank. circuit. Moreover, the range of variation of theresistive component with oscillator frequency is much less than prior systems due to the eliminationof this component at the oscillator central. frequency. r i Y g .If the phase shiftinglnetwork connected across terminals 4 and 5 of Figure 1 is replaced by the network shown in Figure 3A which includes variable inductance 17 and fo e, ge A C nd Ilfcrma l sed t gl T voltage developed between terminal ;1 4 and.-6 isthe feedback voltage applied between the grid 15 and cathode 11 of valve 3 and is identified as voltage E. f

It will be apparent that if capacitor 13 is a iusted to have a wis alfio t e ta ce o res to Ha the central frequency of oscillator ;1, voltages C and D will be equal in magnitude and voltage E will be;ex actly 90f out of phase with voltage A. In other words; the feedback voltage applied between grid 15 and cathode 11 is exactly 90 out of phase with the plate voltage of valve 3. A By adjusting capacitor 13 it is, of course, possible to adjust this phase angle in either directionabout 90. Y Therefore, when the oscillator is operatingat its central frequency, the phase shift is exactly 90f; and no resistive component is injected into tank circuit 9. V When a modulating signal is supplied to grid 2, an apparent reactance is introduced intoytank circuit 9 and its resonant frequency is changed. Consequently, the reactance of capacitor 13 also c hanges, and voltage C-and D are no longer equal. However, as will be-seen from Figures 2A and 2B, the magnitude of voltage E d o esnot change with frequency, since voltage E is a vectorwhich represents the radius of azcircle centered attteminal- 6 and having a circumference extcnding-throughjterminal 4; s and 14. I L As the capacitor reactanpe;hanges withjfrequency, however, the phase angle between voltagesE andA is no longer; 90 butis shifted to 'a somewhat larger or smaller angle depending on the directioncin whichthe oscillatorv resistance 12 in series connection, the operation of the arrangement of Figure '1 will be exactly the same as will be seen from the vector diagram shown in Figure, 3B.

In Figure 3B, H. represents the voltage across the inductance 17 and all other voltages are identified in the same manner as before. Since the reactance of an inductance increases with increasing frequency, the vector diagrams-shown in Figure 2B and Figure 3B areequivalent and result in the same type of circuit operation.

If'thephase shifting network connected across terminalsp4 and 5 of Figure 1 is rearranged as shown in Figure 4A, the circuit will operate as before except that the resistancecomponent is positive when the oscillator fre- .quency-exceeds the central frequency and isnegative when the oscillatonfrequency falls .belowthe central frequency. Figure 4B shows thefvector relationshipsestablished by this rearrangement.

Anotherform 'of the phase shifting networkis shown in Figure 5A andpincludes resistance. 12 and variable inductance 17 in seriahconnection. The resulting .vector diagram is shownjin-FigurejB. Comparison ofFigures 4B and 5B will show that these twodiasrams are equivalent and result in the; same type of circuit operation.

Figure 6 shows a slightly different arrangement of Figure 1 wherein the tube 3 does not shunt the entire tank, but rather only shunts the section of inductance 7 included between terminals 4 and 6. The coeflicient of coupling between the shunted and unshuntedsections of inductance 7 is chosen to be substantially unity. Consequently, the effect of .tube3 is reflected from the shunted section into the unshunted section, and the circuit operation is identical with that shown in Figure 1. c

As will be apparent from the foregoing discussion, our single reactance tube arrangement greatly reduces the magnitude 'of' the resistive component and therefore re- I duces the undesirable amplitude modulation in-like other. I

Figure 7 shows one such arrangement. Valve island its associated phase shifting network are connectedacross the tank circuit 9 in like manner to the connection shown in Figure 1. Valve 3 has its anode-cathode circuit connected across the tank in reverse sense with respect to valve 3'. A second network consisting of resistance 12 and variable capacitor 13 is connected between terminals 4 and 5, and the junction 14' of this resistance and capacitor is connected to the control grid 15' of valve 3'. The incoming modulating signal is applied in push-pull across terminals 2 to drive valves 3 and 3' accordingly,

Capacitors 13 and 13 are adjusted so that the gridplate phase shift for each valve is set for 90 at the oscillator central frequency. Consequently, the control grids of these two valves are effectively in parallel. (The two networks which include respective resistances 12 and 12 and respective capacitors 13 and 13' are required because of the variation in valve characteristics. In the event that both valves had identical characteristics, only one network would be required.)

The vectorial relationships of the voltages applied to valve 3 are shown in Figure 2A. The relationships of the voltages applied to valve 3' are the same except that the voltage A is reversed in direction due to the 180 phase shift between the plate voltages of these valves.

It will be apparent that as the oscillator frequency is shifted to either side of the central frequency, one valve injects a positive apparent resistance into the tank circuit while the other valve injects a negative apparent resistance into this circuit. Since the magnitudes of these apparent resistances are approximately equal, the desired cancellation takes place.

Moreover, by virtue of the push-pull operation, the direct current drifts of the two valves substantially can cel each other, reducing central frequency drift; the effects of changes in operating voltages are substantially reduced; and the oscillator frequency shift for a given change in the modulating signal is sharply increased.

Figure 8 shows a slightly different arrangement of Figure 7. Valve 3 is connected across one half of inductance 7 while valve '3' is connected in reverse sense across the other half of this inductance. Due to the very high coefficient of coupling between both halves of the inductance, the apparent resistance injected into one half section is reflected into the other half section and again cancellation takes place.

From consideration of Figures 2, 3 and 4, it will be seen that it is possible to drive the control grids of valves 3 and 3' in push-pull and connect the anode-cathode circuits of these valves in push-push; cancellation will then take place as before.

Figure 9 shows one such arrangement. The platecathode circuits of both valves are connected in parallel. The control grid of valve is connected to the junction 14 of resistance 12 and variable capacitor 13'. The control grid of valve 11' is connected to the junction 14 of resistance 12' and variable inductance 20.

The vectorial relationships for valves 3 and 3' are shown in Figure 2A and Figure 513 respectively. It will be seen from these figures that the desired cancellation must occur.

While we have shown and pointed out and described the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is our intention therefore, to be limited only as indicated by the scope of the following claims.

We claim:

1. In combination, an inductance; a network connected across said inductance and including in serial connection a resistance element and a reactance element; and an electric discharge valve provided with anode, cathode and control grid electrodes, one of said cathode and grid electrodes being coupled to the junction of said elements,

the other of said cathode and grid electrodes being. coupled to said inductance at a point intermediate theends thereof, the anode-cathode discharge path of said valve shunting said inductance.

2. In combination, 'an inductance; a network shunting said inductance and including in series connection a resistance element and a reactance element; an electric discharge valve provided with anode,cathod e and control grid electrodes and circuits therefor; means connecting the anode-cathode circuit of said valve across said inductance; and means coupling the grid-cathode electrode circuit of said valve between 'the junction of said .-elements and a point on said inductance intermediate its ends. I

3. The combination-as set forth in claim 2 wherein said reactance element is a capacitance. V

4. The combinationas set forth in claim 2 wherein said junction is coupled to said control grid and said inductance point is coupled to said cathode.

5. The combination as set forth in claim 2 wherein said inductance point is the inductance midpoint.

6. The combination as set forth in claim 2 wherein said reactance element is an inductance.

7. In combination with an oscillator provided with a tank circuitincluding in parallel connection an inductance and a capacitance, a reactance tube device responsive to an incoming control signal and comprising an electric discharge valve provided with an anode, a cathode and first and second control grids; means connecting the valve dischargepath across said inductance;

a'network including a resistive and a capacitive element in series connection; means connecting said network across said inductance; means coupling said first grid to the junction of said elements; means coupling said cathode to said inductance at its midpoint; and means to supply .said control signal to said second control grid.

8. The combination as set forth in claim 6 wherein one element in said network is variable.

9. In combination, an inductance; a network shunting said inductance and including in series connection a resistance element and a reactance element; an electric discharge valve provided'with anode, cathode and control grid electrodes and circuits therefor; means connecting the anode-cathode circuit of said valve across a section of said inductance; and means coupling said control grid to the junction of said elements.

10. In combination with an inductance, first and second electric discharge devices, each device being provided with anode, cathode and control electrodes and circuits therefor, the anode-cathode circuits of said devices being connected across said inductance in push-pull connection, a network including in series a resistance and a reactance, said network shunting said inductance, and means coupling the grid-cathode electrode circuit of each device between the junction of said resistance and a point on said inductance intermediate the ends thereof.

11. In combination with an inductance, first and second electric discharge devices, each device being provided with anode, cathode and control electrodes and circuits therefor, the anode-cathode circuits of said devices being connected across said inductance in push-pull connection; first and second networks, each network being connected across said inductance and including in series a resistance element and a reactance element; means coupling the grid-cathode electrode circuit of said first device between the junction of said elements in said first network and a first joint on said inductance intermediate the ends thereof; and means coupling the grid-cathode electrode circuit of said second device between the junction of said elements in said second network and a second intermediate point on said inductance.

12. Apparatus for varying the resonant frequency of a tank circuit in accordance with an incoming signal,

said-"Flask circuit'including an inductance shunted by a 'capacitance,"said apparatus comprising first and second "electric discharge devices, each device provided with an anode, a cathode, and first and second control grids and circuits therefor; means connecting the anode-cathode circludingresistance and capacitance elements in series connection, one of said elements being variable; means cou- 'pling the cathodes of both devices to the midpoint of i said inductance; means coupling the first grid of said 'firstdevice to the junction of said elements in said first sense, anetwork includingin series a resistance .anda reactance, said network shunting said inductance, and

, means coupling the control grids of both devices to the network and coupling the first grid of said second device 7 to the junction of 'said elements in said second network; ,and means to apply said incoming signal in push-pull to the second control grids of both devices.

13. In combination, an electrically closed loop including in serial connection in the order named first and 1 second inductances, a resistor and a capacitor, said loop further including first and second output terminals respectively connected to the junction of said inductances and the junction of said resistor and capacitor, and first and second input terminals respectively connected to the ends of said first and second inductances remote from the junction thereof; and an electric discharge valve provided with anode, cathode, and control grid electrodes and circuits therefor, the anode-cathode circuit being connected between said input electrodes, the grid-cathode electrode circuit being connected between said output electrodes.

14. In combination with an inductance provided with a terminal point intermediate its ends, first and second electric discharge devices, each device being providedwith anode, cathode and control grid electrodes and circuits therefor, the anode-cathode circuit of said first device being coupled between one end of said inductance and said terminal point, the anode-cathode circuit of said second device being coupled between the other end of .junction of said resistancecand reactance.

15. In combination with an inductance, first and sec- 2 and electric discharge devices, each device being provided with anode, cathode and control grid electrodes and circuits therefor, the anode-cathode circuits of said devices being connected across corresponding half sections of said inductance in push-pull connection; first and second networks, each network being connected across said inductance and including in series a resistance element and a reactance element; means coupling the control grid of said first device to the junction of said elements in said firstnetwork; and means coupling the control grid of said second device to the junction of said elements in said second network.

.16. In combination with an inductance, first and second electric discharge valves, each valve being provided with anode, cathode and control electrodes and circuits therefor, the anode-cathode circuits of each valve being connected in parallel across a section of said inductance; first and second networks connected in parallel across said inductance, said first network including a resistance element and a capacitance element in serial connection, said second network including a resistance element and an inductance element in series connection; means coupling the grid of said first valve to the junction of said in said second network.

' References Cited in the file of this patent UNITED STATES PATENTS 2,248,132 Smith July 8, 1941 2,324,282 Crosby July 13, 1943 2,350,171 Lawrence May 30, 1944 2,356,483 Travis Aug. 22, 1944 2,378,245 Rath June 12, 1945 A 2,424,830 Kenefake July 29, 1947 7' 2,445,508 1948 Beleskas July 20, 

